Electrical synchronous inductor motors, including windingexcited internally-toothed stator poles in surrounding relation to permanently-magnetized externally-toothed rotor structures, have come into extensive use largely because of their precision high-speed synchronous and stepping or indexing capabilities. As is well know, the permanent and electromagnetic magnetic fields which cause the attraction and repulsion effects developed in such motors, and which account for their unique operating characteristics, are directed by the toothed stator pole faces and by the toothed rotor peripheries. Construction of the rotor assembly is of particular importance in such motors, because rotor inertia is critical in determining many of the uses which the motor can serve, because so-called "iron losses" and attendant heating in the rotor so greatly influence the frequency and speed capabilities of the motor, because the amount of distribution of permanent-magnet material in the rotor have such controlling effect in determining the efficiency and torque characteristics of the motor, and because the configurations and the assembly interrelationships of both the magnetic and permanently-magnetized materials of the rotor further govern manufacturing costs, overall motor size and weight, and flexibility in the fabrication of different-length models of the same basic design for purposes of developing different output characteristics.
Generally, the permanent-magnet element of synchronous inductor motors has been in an elongated cylindrical form which is best suited to the intended axial magnetization of most common magnet materials. Collaterally, in efforts aimed at a space-conserving arrangement of the needed toothed pole pieces for such elongated magnets, these end pole pieces have been folded back over the magnet ends, after the fashion of face-to-face cups. The axially-extending peripheral teeth on such pole pieces have in this way been permitted a desirable long length without at the same time increasing the overall length of the rotor and entire motor, but this has been at the related expense of serious inefficiency, particularly the inefficiency resulting from magnetic leakage or shunting effects between the magnet and the closely-spaced enshrouding material of the cup-shaped pole pieces. Compensatory increases in the radial spacing between the magnet and its surrounding pole pieces would only undesirably enlarge the rotor, further increase its inertia, and lengthen lossy flux paths.
Flux-conducting magnetic material of the rotor structures in synchronous inductor motors tends to develop more severe heating and iron losses as the excitation frequencies and speeds and increased, of course. Laminations represent one means for suppressing such losses in many types of electromagnetic devices, and have proposed for use in these rotor structures also, as is shown in U.S. Pat. Nos. 2,105,514 and Re. 25,445, for example. However, rotor laminations pose structural-integrity problems which detract from their effective use in fabrication of thin portions of the aforementioned cup-shaped pole pieces, and, as a result, have instead been mounted around such pieces as radially-thick cylindrical sleeves which unavoidably produce unwanted increases in both inertia and radial size.
The present invention relates to improvements which benefit efficiency, torque, and economy of manufacture of synchronous inductor motors, and in one particular aspect, to novel and improved rotor units for such motors which are wholly laminar, are of relatively short axial length, suppress leakage of magnetic flux, lend themselves to efficient uses at high frequencies and rotational speeds, and are of relatively simple and yet rugged form suitable for low-cost production. The annular permanent-magnet elements utilized in the improved rotor units have relatively small ratios of axial to radial thicknesses, which may be not in excess of 1:3, and in this respect are quite the opposite of the usual elongated cylindrical magnet. Moreover, the toothed magnet pole pieces associated in end abutments with the thin permanent magnet are likewise axially thin, each being made up of a plurality of identical planar annular lamination sheets of magnetic material. The laminated pole pieces exhibit no axial overhang whatsoever in relation to the thin magnet, and the annular magnet extends radially fully out to the roots of the teeth formed on the peripheries of the pole pieces, for optimum utilization of material and minimized flux leakage. In this type of construction, the face areas of the pole pieces and magnet are ample enough to accommodate use of a relatively large and strong nonmagnetic central shaft without undue compromise of magnetic characteristics, such as can be the case with conventional rotor designs. Preferably, all of the pole piece laminations are bonded together in sandwiching relation with the thin permanent magnet by thin layers of a cement such as an epoxy, and their assembly is secured to the shaft in the same manner, such that glued surfaces are of desirably broad area and of resulting high strength. Further, the washer-shaped laminations and magnet advantageously transmit substantially all major forces in direct relation to the shaft, thereby avoiding "facturing" tendencies under conditions of high-speed and other rigorous uses. The short axial lengths of rotor units which can be realized in accordance with these teachings in turn facilitate the doubling, tripling, etc., of such units end-to-end on a single shaft, such that, in cooperation with one form of stator which has also been suitably lengthened, one basic motor configuration can yield corresponding multiples of power output.